1. Field of the Invention
This invention relates to the disposition of earphones on head mounted visors or display apparatus generally. More particularly, but not exclusively, it relates to such disposition on a head mounted display (HMD) adapted for use in virtual reality applications.
2. Description of the Prior Art
Originally virtual reality applications involved the user being surrounded by a projected image or a plurality of video monitors. Stereoscopic sound effects could be provided readily by conventional hi-fi speaker systems. Latterly, head mounted displays have become the norm in which the virtual image is displayed by means of a pair of small video screens viewed through binocular optical devices. These HMD's have been extremely bulky and are generally in the form of a helmet lowered on to the head of a user. Such helmets generally have sufficient internal space to mount small speaker drivers positioned to be adjacent and spaced apart from the ears of a user.
Large HMD's of helmet form have various disadvantages associated with their bulk and weight. In particular the virtual illusion is to some degree detracted from as a consequence of wearing an HMD because the wearers head appears to have a greater weight and moment of inertia than it would have in real situations. Consequently, it has long been desired to provide a lightweight HMD more akin to a visor comprising an adjustable head band fitting closely about the head of a user. Recent advances in miniature video screen and optics technology have made this a feasible proposition. However, proposed lightweight HMD's lack the internal space of the prior helmet type designs. Consequently, they provide no room to mount small speaker drivers.
To overcome the space limitations of lightweight HMD's it has been suggested that small earphones, commonly used with WALKMAN (.TM.) type cassette players, could be mounted on the inner side faces of the head band. However, clear sound reception from small earphones requires that they are accurately aligned with the ear canals of a user. Hence because a head band must be adjustable to fit different head sizes a generally central disposition of the earphones suggests itself.
Unfortunately, anthropomorphic models of different human head sizes illustrate that the relative dimensions of the human head are not constant from one subject to another. In particular, the position of the ear canals relative to the bridge of the nose and rear of the skull will vary from person to person. Consequently, there can be no optimum position on an adjustable head band at which to place small earphones. To overcome this the obvious solution is use miniature headphones separate from the HMD which may be positioned independently thereof.